i honestly dont know the cause, because even though mealworms are more fatty than crickets, live mealworms still only have ~12% fat content. Double that of crickets yes, but nothing thats going to spike a mix into unsafe levels.
Like, even if live mealworms made up 10% of your hedgehogs diet. If we consider the maximum recommended guidelines for kibble as 35% protein and 15% fat, and take the average GA for live mealworms as being 20% protein and 12% fat, the total GA for a diet composing of 10% live mealworms and 90% kibble would be 33.5% protein & 14.7% fat. < the live mealworms would actually lower
(albeit slightly haha) the fat content, not increase it.
I'm not viewing your response as an argument haha, dont worry - i've always just been genuinely curious as to where the advice for limiting mealworms so drastically came from, or if it was just something that just kept being passed along the vine and nobody ever questioned it, which explains why it's still tossed around.
Some hedgehogs, like you said, gain weight easily so I can see advice for lower fat diets and limiting mealies in that regard. But generally speaking, for any average, active hedgehog; i don't see reason to limit worms to a weekly treat instead of a daily inclusion of the diet at all (personally anyways). Within reason, of course.